Expenses of the rental of a property are deductible against the rent received regardless of your income.
Whether or not a net loss from a rental property is deductible against your other income may depend on your adjusted gross income when the rental income is passive income.
Form 8582 is used to compute how much of up to $25,000 may be allowed of a net passive loss against your other income. Generally, for modified adjusted gross income of more than $150,000 none of the passive loss can be deducted against ordinary income. Those losses are suspended until you have pssive income or you completely dispose of the passive activity.
For more information, see this article and Instructions for Form 8582
Yes, the interest to buy build or acquire the rental is part of the rental property expenses.
I hope this helps to clarify.